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I have a Galaxy S I9000 (2.3.6, Gingerbread.XXJW4) and use my phone minimally (mostly just on standby). I would like a least a couple of days, and hopefully a week or two between recharges if possible (like my old crappy phone with a smaller battery).

There's already been reports that lowering the CPU frequency using something like SetCPU (needs root) can increase battery life, along with apps like 'Disable Service' to freeze stubborn apps. And this thread gives some sound advice for reducing battery usage further.

But I'm wondering if a custom ROM can bring battery life conservation up a level. I've been researching for the lightest ROM, and one called 'Simplicity' seems the most promising (Slim Bean, CyanAOSP, Vanilla RootBox, DarkyROM and C-RoM Mix are other contenders). However there are also reports that the stock ROM is best for battery life, in which case none of these custom ROMS would be worth bothering with for me. On the other hand, many people in that thread are reporting great battery life, with some lasting over 2 or even 3 days (I currently get just over half a day).

I am mostly thinking about processes/services such as "Android System" and "Android OS", as they rise to the top of CPU usage for me. Would these have the potential to be lighter on the battery with a custom ROM compared to the stock ROM on my I9000? How about "Wi-Fi", "Cell standby", "gpsd", or even "Phone idle"?

More information is found here, though it's not quite the same question, and I'm not fully convinced with the highest rated answer there yet (not mentioning CPU reclocking or aforementioned processes such as a lighter "Android System" process potentially).

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closed as not constructive by Izzy, onik Apr 8 '13 at 8:58

As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance.If this question can be reworded to fit the rules in the help center, please edit the question.

Sorry, but "more than a week" is very unlikely to achieve (unless you run exclusively in airplane mode with a lot of other services disabled as well, and have no SIM card in your device). As soon as you put a SIM card into your device, a couple of days is the most you can achieve. Enable data service, and more than 3 days are unlikely already. // This question is also not good fit for our site, as it is not easily answerable by "simple facts", but rather leads to discussions. I'd recommend to ask this at e.g. XDA developers. – Izzy Apr 8 '13 at 8:30
Maybe that's me being too optimistic, but if my old phone last two weeks, then maybe a custom ROM can emulate that simplicity and make the "Android System" and "Android OS" processes much lighter. That's still a possibility, and I think I have heard some reach more than a week - I'll go hunting... – Dan W Apr 8 '13 at 8:38
I've tried a lot, 8 days was max (with above measures). And "old dumb phones" lasting 2 weeks have other specs: smaller display, less powerful other hardware components. You cannot compare that. // take a look at the battery-life tag wiki and its most frequented questions to get some ideas. – Izzy Apr 8 '13 at 8:45
It was CyanogenMod (CM7) on my HTC Wildfire (aka Buzz). I assume I would almost reach the same values with CM7.2 on my Milestone²: Currently running it with SIM, 2-3 voice calls (~2min each) daily, no data services, Wifi at home. Get up at ~8 am, go to bed ~ midnight with 90%+ left. Of course, I've disabled some stuff, e.g. frozen Google Maps which otherwise was permanently running in background without ever being started by myself. // Pick anything that comes as "plain Vanilla" as possible, and no bloatware. – Izzy Apr 8 '13 at 9:00
The idea that 'Android System' and 'Android OS' can be made more lightweight by a custom ROM is flawed. If you seem one of them in the battery usage list then it's usually because of background data (sync). Simply disabling background data will then make those processes less CPU-intensive, but that can be done on stock/vanilla Android too. You don't need a ROM for that. I also encourage you to hang around in chat to discuss the topic. – Flow Apr 8 '13 at 9:42